Ground based beam forming with clustering

ABSTRACT

A system and method for beamforming includes providing an antenna including feeds, a coverage area including service areas and data streams for each of the service areas; selecting a cluster of M feeds from the feeds; computing, with a GBBF processor (ground based beam former), M×N weights; generating M feed excitations by distributing the N data streams per the M×N weights; switching an array to transfer a respective one of the M feed excitations to a respective one of the M feeds; and beamforming, with the M feeds of the antenna, N beams. In the method, the N beams are each focused on a respective service area of each of the N data streams, the M×N weights improve the transmitting into the respective service area of each of the N data streams, and at least one of the N beams includes a portion of a plurality of the M feed excitations.

CROSS-REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE

The present application is a continuation of U.S. application Ser. No.17,247,224, filed Dec. 4, 2020, which is incorporated herein byreference in its entirety.

FIELD

A system and method using on-board switched feed clusters for a systembased on Ground-Based Beam Forming (GBBF). The on-board switchingreduces GBBF feeder link requisites.

BACKGROUND

On-board beam forming direct radiating phased arrays are extremelydifficult at Very High Throughput Satellite (VHTS) scales. VHTS on-boardbeam forming with array fed reflectors are somewhat more realizable, butstill very complex. GBBF systems move the beam forming complexity to theground where it is more easily handled. The roadblock to VHTS GBBF hasbeen the feeder link bandwidth needed to support the very large numberof feeds (antenna elements) on a VHTS. The very large number of feeds inthe VHTS GBBF is impractical as the feeds need an enormous amount ofbandwidth. Optical bandwidths can address this, but optical has its ownset of challenges.

BRIEF SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that is further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

The present teachings systemically serve user terminals in a very HighThroughput Satellite (VHTS) system via on-board switched feed clustersusing Ground-Based Beam Forming (GBBF). The present teachings addressthe large required feeder link bandwidth of a GBBF system. A VHTS mayhave a large number of feeds, and it may be infeasible to provide enoughfeeder link bandwidth to address all the feeds at the same time. In thepresent teachings a subset of the feeds is used within any one time step(transmission interval) so that a limited amount of feeder linkbandwidth suffices.

A system of one or more computers can be configured to performparticular operations or actions by virtue of having software, firmware,hardware, or a combination of them installed on the system that inoperation causes or cause the system to perform the actions. One or morecomputer programs can be configured to perform particular operations oractions by virtue of including instructions that, when executed by dataprocessing apparatus, cause the apparatus to perform the actions. Onegeneral aspect for a method for beamforming includes providing anantenna including feeds, a coverage area including service areas anddata streams for each of the service areas; scheduling N data streams ofthe data streams, selecting a cluster of M feeds from the feeds;computing, with a GBBF processor (ground based beam former), M×Nweights; generating M feed excitations by distributing the N datastreams per the M×N weights; switching an array to transfer a respectiveone of the M feed excitations to a respective one of the M feeds; andbeamforming, with the M feeds of the antenna, N beams. In the method,the N beams are each focused on a respective service area of each of theN data streams, the M×N weights improve the transmitting into therespective service area of each of the N data streams, and at least oneof the N beams includes a portion of a plurality of the M feedexcitations.

The method where the antenna includes an array-fed reflector includingmore than the M feeds. The method where M is greater than N. The methodwhere the M×N weights are weighted to account for a predicted offeredtraffic demand based on a usage pattern for each of the N data streams.The method where the scheduling, the selecting, the generating, theswitching and the beamforming are performed per an integral multiple ofa transmission interval. The method where the scheduling moves the Nbeams over a breadth of the coverage area over a plurality oftransmission intervals. The method where the selecting includes a staticmapping of clusters to a subset of service areas, where each subsetincludes N service areas and each subset includes uniformly spacedservice areas. The method where the selecting selects feeds associatedwith a respective service area of one or more of the N data streams. Themethod may include forming the N data streams by encoding, modulatingand framing each of the N data streams.

The method may include sending the M feed excitations to a satellite,where the switching and the beamforming are performed in the satellite,and the beamforming includes transmitting the N beams from the antenna.The method may include receiving the M feed excitations from asatellite, where the switching and the beamforming are performed in thesatellite, and the beamforming includes receiving the N beams from theantenna. The method may also include where the M×N weights provideinterference suppression so that a same frequency and polarization isused for the M feeds in the cluster. Other technical features may bereadily apparent to one skilled in the art from the following figures,descriptions, and claims.

In one aspect, a system to beamform includes an antenna including feeds,a coverage area including service areas and data streams for each of theservice areas, a Scheduler to schedule N data streams of the datastreams and to select a cluster of M feeds from the feeds, a GBBFprocessor (ground based beam former), to compute M×N weights, a ComplexWeight Multiplier to generate M feed excitations that distribute the Ndata streams per the M×N weights, and a switch to transfer a respectiveone of the M feed excitations to a respective one of the M feeds. In thesystem, N beams are beamformed with the M feeds of the antenna, the Nbeams are each focused on a respective service area of each of the Ndata streams, the M×N weights improve the transmitting into therespective service area of each of the N data streams, and at least oneof the N beams includes a portion of a plurality of the M feedexcitations.

Additional features will be set forth in the description that follows,and in part will be apparent from the description, or may be learned bypractice of what is described.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features may be obtained, a more particular descriptionis provided below and will be rendered by reference to specificembodiments thereof which are illustrated in the app ended drawings.Understanding that these drawings depict only typical embodiments andare not, therefore, to be limiting of its scope, implementations will bedescribed and explained with additional specificity and detail with theaccompanying drawings. Throughout the drawings and the detaileddescription, unless otherwise described, the same drawing referencenumerals will be understood to refer to the same elements, features, andstructures. The relative size and depiction of these elements may beexaggerated for clarity, illustration, and convenience.

FIG. 1 illustrates a Very High Throughput Satellite (VHTS) systemincluding Ground-Based Beam Forming (GBBF) according to variousembodiments.

FIG. 2A illustrates a beam illumination for a coverage area according tovarious embodiments.

FIG. 2B illustrates a beam illumination for a coverage area according tovarious embodiments.

FIG. 3A illustrates a cluster aimed over a first location within acoverage area for a transmission interval according to variousembodiments.

FIG. 3B illustrates a cluster aimed over a second location within acoverage area for a transmission interval according to variousembodiments.

FIG. 4 illustrates a cluster and feeds according to various embodiments.

FIG. 5 illustrates a processing center according to various embodiments.

FIG. 6 illustrates a Radio Frequency Transmitter (RFT) site inaccordance with one embodiment.

FIG. 7 illustrates a satellite block diagram in accordance with oneembodiment.

FIG. 8 illustrates an aspect of the subject matter in accordance withone embodiment.

FIG. 9 illustrates an aspect of a multiport power amplifier or SSPAarray in accordance with one embodiment.

FIG. 10 illustrates clusters to cover the continental United States inexemplary embodiments.

FIG. 11A illustrates an exemplary feed array and cluster according tovarious embodiments.

FIG. 11B illustrates an exemplary feed array and cluster in accordancewith one embodiment.

FIG. 11C illustrates an exemplary feed array and cluster in accordancewith one embodiment.

FIG. 12 is a block diagram of contributors to calibration errorsaccording to exemplary embodiments.

FIG. 13 illustrates an aspect of the subject matter in accordance withone embodiment.

FIG. 14 is an exemplary scheduling flow chart according to oneembodiment.

FIG. 15 illustrates an aspect of the subject matter in accordance withone embodiment.

FIG. 16 illustrates an aspect of the subject matter in accordance withone embodiment.

FIG. 17 illustrates a method for beamforming according to variousembodiments.

DETAILED DESCRIPTION

The present teachings may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as SMALLTALK, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present invention, as well as other variations thereof, means that afeature, structure, characteristic, and so forth described in connectionwith the embodiment is included in at least one embodiment of thepresent invention. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

Introduction

The present teachings systemically serve user terminals in a very HighThroughput Satellite (VHTS) system via on-board switched feed clustersusing Ground-Based Beam Forming (GBBF). In some embodiments, a feed maybe an antenna element. As such, a feed pattern may be an elementpattern. In some embodiments, a beam pattern may be a combination offeed patterns. A Beam pattern may be formed by applying differentamplitudes and phases to the same beam signal to derive multiple feedsignals in the forward downlink. This may be performed by multiplying abaseband signal by complex weights. The set of all multiplications is anM×N matrix with N beam inputs and M feeder link outputs. Thus, each beamsignal goes to multiple feeder links and each feeder link signalcomprises multiple beam signals. A beam pattern may be smaller than afeed pattern.

In some embodiments, a transmission interval or hop may be a timeinterval during which a specific set of beam patterns are formed. Theset of beam patterns may change from one hop to the next, usually in anintegral multiple of the transmission interval.

A Service area of a beam is the area in which users being served duringa hop are located. The service area tends to be located near the peak ofthe beam. In other words, the size of the service area is small enoughso that the directivity of the beam at the edge of the service areamight be less than a dB reduced from the directivity of the beam at thecenter of the service area. In a traditional single feed per beamarrangement, 4 to 6 dB of directivity loss would be typical and theservice area would be a much larger fraction of the beam area. A beampattern may peak over a service area and have nulls over other serviceareas.

In some embodiments, on any hop, about 80-85 beam patterns are formedfrom the 99 selected feeds. They beam patterns serve about 80-85 serviceareas. According to various embodiments, the service areas have gapsbetween them and are not contiguous. Users located in the gaps cannot beserved during that hop and wait their turn on a later scheduled hop. Insome embodiments, during a hop, 99 feeds may be active. These feeds tendto be contiguous in the feed plane on the satellite. However, the feedschosen during a hop are need not be contiguous. The non-contiguous feedsmay be exception cases caused by scheduling demands, reserved beams,etc. Each feed receives a feed excitation signal from one of the feederlinks from the processing center.

FIG. 1 illustrates a Very High Throughput Satellite (VHTS) systemincluding Ground-Based Beam Forming (GBBF) according to variousembodiments.

A VHTS system 100 including a Ground-Based Beam Forming (GBBF) processor102 may be connected to the internet 108. In a forward direction 104(for example, from internet-to-customer) data streams containing digitalrepresentations of the Feed excitations 124 are formatted fortransmission over a Fiber Network 110. In some embodiments, in a returndirection 106 (for example, from customer-to-internet) data streamscontaining digital representations of the Feed excitations 124 areformatted for transmission over the Fiber Network 110. A feed excitationis the signal that will be transmitted in a downlink 118 from asatellite 116 to a UT 122. The Feed excitation 124 is distributed viathe Fiber Network 110 to a network of RF GWs 114 via links 112. The RFGWs 114 convert the digital baseband data of the feed excitationreceived over links 112 into RF signals and transmit them to a satellite116. The satellite 116 converts the Feed excitations 124 to the forwarddownlink frequencies and routes the signals to a selected subset offeeds. These feed transmissions produce beam patterns as the downlinks118 of the satellite 116 covering the UTs 122.

The present teachings differ from traditional “bent-pipe” forwardsatellite paths in that the processing center includes a GBBF. Thesatellite 116 includes an antenna and feed configuration suitable foruse with a GBBF. The information transmitted to the RF GWs 114 (and thesatellite 116) are feed excitations for transmission by the satellite116 to the UTs 122, whereas in a bent pipe satellite informationtransmitted to the RF GWs 114 (and the satellite 116) would be beamsignals.

The present teachings differ from a traditional GBBF in that the feedexcitations are limited to a small subset of the total feeds on thesatellite at any given time. This enables the satellite to support manyfeeds without a proportional increase in the bandwidth. The subset mayform a contiguous “cluster” of feed where all the feeds are “touching”.In one embodiment, the subset may form two or more groups of varyingsizes. In some embodiments, a cluster may include not contiguous feeds,for example, to schedule outlier/latent feeds that did not scheduled.Restrictions and limitations on the subset are discussed below.

A satellite 116 may include an antenna (not shown) including feeds, forexample, X feeds. One or more of the feeds may be activated at a timefor transmission or reception. In one embodiment, M selected feeds outof the X satellite antenna feeds may be activated to service N beams(for reception or transmission) at a time.

FIG. 2A illustrates a beam illumination for a coverage area according tovarious embodiments.

A coverage area 200 includes service areas. A service area 202 and aservice area 204 may be serviced/illuminated during a transmissioninterval. Service area 202 and service area 204 are not contiguous. Theremaining hexagons (service areas) of FIG. 2A may be served on differenttransmission intervals. The circle 206 and 208 may roughly correspond tothe contour where the beam for the service area 202 and service area 204has reduced by 6 dB or more. An exemplary circle 214 may correspond tothe contour where the beam for the service area 202 has reduced by 3 dBor more.

A cluster of service areas may be illuminated by beams from a satellite(not shown) within the satellite's coverage area. Exemplary dimensionsof the cluster may be in (U, V) coordinates as seen from a geostationarysatellite. In some embodiments, a diameter of the circle 214 may beroughly the half-power beam width of a 5 m antenna at Q-band (40-42GHz). The 5 m antenna may be a direct radiating array or an array-fedreflector. In some embodiments, the array-fed reflector may use farfewer active feeds than a direct radiating array. The feeder linkbandwidth may be proportional to the number of active feeds.

Service areas may be spaced so that the same frequency and polarizationcan be used in the cluster during the same transmission interval usingan interference suppression provided by the GBBF processor. The numberof service areas in the cluster during a transmission interval dependson the number of feeds used in the cluster, the desired spectralefficiency, the traffic destined to the customer terminals within theservice area, and other factors related to priority and efficiency. Theservice areas for a cluster on a given transmission interval may beuniformly spaced as shown or they may be more randomly distributed.

FIG. 2B illustrates a beam illumination for a coverage area according tovarious embodiments.

In some embodiments, the on-board switching may create 16⁹⁹ combinationsof clusters from the active feeds. Each combination is called a cluster.Only one combination is formed on each hop. Once a cluster of 99 feedsis chosen, the beam patterns are formed. Selecting a set of 99 feedsdoes not fully determine the beams or service areas. FIG. 2A and FIG. 2Bdiffer by choosing one service area differently and moving the beam tocover that service area. The same set of 99 feeds may be used in bothcases. In other words, the same cluster may serve different Serviceareas. For example, in FIG. 2B service area 202 and service area 210 maybe served by the same cluster as service area 202 and service area 204of FIG. 2A.

FIG. 3A illustrates a cluster aimed over a first location within acoverage area for a transmission interval according to variousembodiments.

FIG. 3B illustrates clusters aimed over a second location within acoverage area for a transmission interval according to variousembodiments.

FIG. 3A and FIG. 3B illustrate a coverage area 306 (here the easternhalf of the continental United States), a first location 302 serviced bya cluster and a second location 304 serviced by a different clusterduring two transmission intervals. The axes of FIG. 3A and FIG. 3B arein (U,V) coordinates for an antenna on a geostationary satellite with anantenna boresight at approximately 306. By moving a cluster, thecoverage area can be serviced over a multiplicity of transmissionintervals. In some embodiments, the service areas within a cluster maybe moved (shifted) with or without moving the overall cluster. The shapeof a coverage area need not produce circular clusters everywhere, forexample, Florida in the United States. The set of feeds chosen for anyindividual transmit interval may be chosen to account for this. As notedpreviously, the clusters need not be contiguous.

FIG. 4 illustrates a cluster and feeds according to various embodiments.

A cluster 400 may include feed secondary patterns 402. Each feedsecondary pattern 402 may be associated with a feed and may have acorresponding center of secondary pattern 404. By convention, asecondary pattern is the illumination pattern formed on the surface ofthe earth by the energy transmitted by that feed after reflection offthe satellite transmit antenna. The feed secondary pattern 402 isrepresented by a circle in FIG. 4 but the actual pattern may have a morearbitrary equal power contour.

One or more feed secondary patterns may combine to service a servicearea. For example, service area 82 406 may be combination of adjacentfeed secondary patterns 408. Due to the combining of feed secondarypatterns, the service areas do not have a fixed relationship to thecenters of the secondary patterns. A GBBF computes the beam formingweights for each feed to improve the transmission into the serviceareas.

Processing Center

FIG. 5 illustrates a processing center according to various embodiments.

The processing center 500 for the forward direction includes a Scheduler502, a GBBF 504, a Complex Weight Multiplier 508, service area queues510, a Modcod/frame generator 506, an Internet feed 512, a Feeder linkdistributor 514 and a combiner 516. a data 518, a queue status 520, an Nbeams Metadata 522, an N beam data 524, an EsNo prediction 526, an EsNoReports 528, an N beam superframes 530, a M×N Complex Weights 532, aChannel State 534, a Calibration Reference 536, and an M feedexcitations 538.

Data 518 destined for the customer enters from the Internet feed 512 maybe queued at a respective service area queue 510. In some embodiments,Internet feed 512 may be a 400 Gbps data rate feed for one polarization,for example, the right hand circularly polarized (RHCP). An additionalInternet feed 512 may be handled in an identical and independent systemgenerating LHCP data. Notionally, the processing center 500 could be asingle site or one site for each polarization in the forward direction.

Data 518 is queued by service area each transmission interval. Thesystem may be presumed to operate on a fixed transmission interval,sometimes referred to as a “hop”. During each transmission interval, theScheduler 502 examines the queue status per queue status 520 anddetermines which queues should be served. As in traditional queueingsystems, the status may include the queue depth, information priority,and age of the packets. The teachings may include a location of theservice areas, as the service areas may dictate the feeds to be usedduring this transmission interval. This process is described in moredetail in the “Scheduling” section below.

Once the feeds and service areas have been selected, the GBBF 504computes the beam weights using for example, minimum mean square error(MMSE) beam forming. To perform these calculations, the GBBF 504 uses Nbeams Metadata 522 and Channel State 534 the channel state informationfor each data path. This information may be generated by a calibrationsubsystem described in more detail in the “Calibration” section. Theoverall beam forming computations and processing is described in moredetail in the “Beam Forming” section.

The GBBF 504 may have two outputs, namely, EsNo prediction 526 and M×NComplex Weights 532 (w_(ij)). EsNo prediction 526 predicts the linkperformance at each UT so that an appropriate modulation and coding(modcod) can be selected to assure correct delivery of the data to thecustomer. M×N Complex Weights 532 is the beam weights used in the beamforming computation.

Data is dequeued from the service area queues 510 as selected by theScheduler 502 and validated by the GBBF 504. The system may operate withsuperframes, which may be constructed by computing the EsNo at each(presumed known) location to be served for ModCod assignment. The EsNocomputing may be based on EsNo Reports 528 from UTs combined with thepredictions from the MMSE beam forming computations. The Modcod/framegenerator 506 forms codeblocks that will fit into a superframe for eachselected service area queues 510.

Then M×N Complex Weights 532 w_(ij), may be used by the Complex WeightMultiplier 508 to multiply the dequeued data streams i to form or feedexcitations j. ƒ_(j)=Σs_(i)w_(ij). The combiner 516 may inject acalibration underlay signal based on the Calibration Reference 536(per-feed per-band) to each feed transmission to enable the calibrationfunction mentioned above. The final step is to format this dataappropriately for transmission over the links to the RF gateways usingthe Feeder link distributor 514 to generate the M feed excitations 538.

Fiber Network and Radio Frequency Transmitter

FIG. 6 illustrates a Radio Frequency Transmitter (RFT) site inaccordance with one embodiment.

An RFT site 600 includes a fiber interface 602, a Fiber to IF 604, an IFto Band 606, a Band amplifier 608, a Baseband to fiber 610, a Band to IFDemodulator 612 and a band LNA 614. Data 616 formatted as a feed (forexample, one of the M feed excitations 538 from the processing center500 of FIG. 5) is received by the RFT site 600 for transmission to thesatellite. Notionally, data 616 is communicated with the RFT site 600over a redundant fiber network.

In the forward direction, data 616 from the fiber interface 602 isconverted to a convenient intermediate frequency (IF), such as 6 GHz, atthe Fiber to IF 604 block and then upconverted to the final RF frequencyat the IF to Band 606 block (for example, V-band, E-band, or the like)which is transmitted by the Band amplifier 608. In the return direction,a reverse process is undertaken.

Satellite

FIG. 7 illustrates a satellite block diagram in accordance with oneembodiment.

A satellite 700 comprises a low-noise amplifier (LNA) 702, a Switch 704,an SSPA Array 706, a Transmit Antenna 708, an up-converter Amplifier710, an LNA per beam 712 and Receive Antennas 714. The satellite 700receives a UL feeder link 716 from a RF GW which is output as a User DL718. The satellite 700 receives a User UL 720 from a UT which is outputas a DL feeder link 722.

The satellite 700 may be a passive beam former with a beam hoppingcapability. In the forward direction, in some embodiments, the UL feederlink 716 may be V-band (47-51 GHz) and E-band (81-86 GHz) uplinks thatare converted to the User DL 718 for downlink transmission, for example,as Q-band (40-42 GHz) signals. In some embodiments, in the returndirection, the User UL 720 may be Ka-band (28-30 GHz) and converted toE-band (71-76 GHz) for transmission to the RF GW as the DL feeder link722. The conversions may be a single conversion directly from the uplinkfrequency to a corresponding downlink frequency or it may be a dualconversion, first to a convenient IF than back up to the downlinkfrequency. The satellite may incorporate a digital channelizer in the RFchain to allow frequency bands to be conveniently swapped for servicereasons or to facilitate RFT site diversity. Each UL feeder link 716 isrouted to the Switch 704 and then to the SSPA Array 706 and then theTransmit Antenna 708.

FIG. 8 illustrates processing of forward direction feeder links at asatellite according to some embodiments.

The forward direction feeder links 810 at a satellite may include downconversion (for example, to the Q-band) including automatic levelcontrol (ALC) 802 to compensate for fading on the forward directionfeeder links 810. The Switch 804 couples to a multiport power amplifier806. Both the Switch 804 and MPA 806 are integral to implementing theclusters. The Switch 804 routes a single feeder link to one of inputs tothe MPA 806. In the exemplary embodiments, the Multiport Power Amp 806may have 16 inputs.

Considerable flexibility is provided by a simple switching arrangementof multiple Switches 804. In the exemplary embodiments, ninety-nine (99)Switches 804 may be used. In the exemplary embodiments, each Switch 804has one input and 16 outputs. The switching arrangement of 99feeds/switches and one of 16 outputs from each Switch 804 provides 16⁹⁹feed arrangements, not necessarily limited to contiguous clusters. Insome embodiments, roughly 1000 clusters of 99 feeds may provide fullcoverage of the Continental United States (see FIG. 10). Each 1:16switch may be controlled independently, allowing for a flexibleselection of feeds per hop. A baseline cluster mapping may be created,for example, on the order of 1000 clusters. Clusters may be redefinedduring satellite orbit. In some embodiments, the system may select anduse feeds (for example, 99 feeds) without using clusters.

The Switch 804 may be implemented at Q-band with FET switches. Thecontrol signal 818 for each switch may be provided by a control center(not shown). The control signal 818 could be embedded in the uplinkchannels or sent via a separate control channel from the processingcenter to an on-board controller in the satellite.

FIG. 9 illustrates an aspect of a multiport power amplifier or SSPAarray in accordance with one embodiment.

A multiport power amplifier 900 may include a 16×16 Butler Matrix 902, a16×16 Inverse Butler Matrix 904, an SSPA 906, and a feeder link signal908.

The MPA 900 receives a feeder link signal 908 as an input from theswitch on one of its 16 inputs. Only one input is active at any time.The 16×16 Butler Matrix 902 distributes the input signal to the 16 SSPAs906 at different phases. The SSPAs all amplify their signals. The SSPAoutputs are fed to the 16×16 Inverse Butler Matrix 904 that coherentlycombines the SSPA outputs so that the total energy arrives on thecorresponding output port and no energy arrives on any other output.Each output port connects to a satellite antenna feed (not shown), ingeneral through an output filter (not shown). The feed connected to eachport is chosen in a way to assure maximum flexibility. Note that 99feeder links connecting to 16 switch ports provides 16⁹⁹ combinations offeeds to be used on any given hop. This arrangement avoids thecomplexity of connecting each feeder link to every feed and stillprovides a very large number of possible active feed arrangements. Notall feed arrangements need to be clusters.

FIG. 10 illustrates clusters to cover the continental United States inexemplary embodiments.

FIG. 10 illustrates secondary feed pattern centers for 1345 feeds on a 5m antenna with an 8.75 m focal length. Feed diameter is 1.78 cm and thefeed is defocused by 14 cm. When the cluster includes 99 feeds, thecluster is roughly 8% of the total feed count of the continental UnitedStates.

Feed Array

FIG. 11A illustrates an exemplary feed array and cluster according tovarious embodiments.

FIG. 11A and FIG. 11B illustrate exemplary Feed Arrays, Clustering, andFeeder Links where the feed cluster is assumed to be a square including100 feeds. A 32×32 Feed array 1102 may be used to distribute up to 1024feeds. The feeds may be single polarization. In one example, variousclusters 1104 may be formed in the 32×32 Feed array 1102. Feed 1106 maybe addressed as (0,0) in the 32×32 Feed array 1102. Feed 1112 may beaddressed as (31,31) in 32×32 Feed array 1102.

The 10×10 feed clusters 1104 may overlap. Only one cluster may be activeat a time per polarization. The other polarization may be completelyindependent.

FIG. 11B illustrates an exemplary feed array and cluster in accordancewith one embodiment.

FIG. 11B illustrates one possible arrangement of square clusters in asquare feed array to produce 529 distinct clusters (23×23=529). Thecluster 1104 in the upper left corner might be numbered cluster 1, thecluster in the upper right corner might be numbered 23, the cluster inlower left corner might be numbered 506 and the cluster in the lowerright corner might be numbered 529.

FIG. 11C illustrates an exemplary feed array and cluster in accordancewith one embodiment.

The next step may assign feeder links to feeds. In this example, onefeeder link serves (at most) one of 16 feeds at a time. By assigningfeeds to a switch as shown in FIG. 11C, which shows the 16 feedsassigned to one of the switches, each feeder link is associated with themaximum number of clusters. This arrangement maximizes cluster formingflexibility while minimizing the number of feeds associated with afeeder link routing, switching and amplification of the feeds. Each ofthese feeder links is then mapped to a multiport amplifier.

Calibration

FIG. 12 is a block diagram of contributors to calibration errorsaccording to exemplary embodiments.

Calibration is needed to form coherent beams. The system is subject toDoppler frequency and time shifts, frequency drift, phase noise,temperature and other effects on-board as shown in FIG. 12. Theseeffects can reduce the coherency of the multiple feeds contributing to aspecific formed beam. Contributors to calibration error 1200 may includeerrors from a Terrestrial Delay 1202, a GW Frequency Conversion 1204, aUL Doppler Frequency and Timing 1206, a Satellite Frequency Conversion1208, a Satellite Delay Variations 1210, a UL Atmospheric Effects 1212,a Satellite Antenna Pointing and Shape 1214, an end-to-end frequencyslope 1216, a VSAT drift during measurement 1218, and a Feed Excitation1220. The present teachings use an end-to-end approach.

FIG. 13 illustrates processing for calibration errors at a UT accordingto some embodiments.

In some embodiments, calibration may be done on the satellite usingembedded information in the feeder link signals. The Processing Center(PC) may inject per-feed calibration signal after the beam former. Thissignal carries through the end-to-end system and arrives at the UT. TheUT knows the calibration format and correlates a local reference againstthe received signal as shown in FIG. 13.

A UT 1300 may include a module to account for various Delays 1302 basedon a calibration reference 1304 and a symbol timing error 1306 that isoutput as signal 1308. A combiner 1310 combine signal 1308 with User DL1312 (possibly after being converted to Q-band) to generate a phase andamplitude error 1314.

In some embodiments, the UT reports per feed measurements of thecalibration signals to the processing center. For the reporting, The UTmay look at the full expected bandwidth of the user DL 1312 (forexample, 2 GHz), independent of the bandwidth received at the UT.Correlation may be performed for each sub-band in the full expectedbandwidth. This process may be repeated for 99 feeds forsingle-polarization UTs, 198 if UTs are dual-polarization. Symbol timingmay be dithered until correlation peak is maximized.

The PC receives the relative phase and amplitude 131 reports for eachfeed on each hop from designated UTs. The PC may determine complexerrors for each feed. In some embodiments, the PC may determine asatellite antenna pointing error. The PC may determine appropriatecorrection factors considering system nonlinearities. The PC may applyphase error compensation and antenna pointing corrections at baseband.The PC may command the satellite ALC to correct amplitude errors.

Beam Forming

In some embodiments, beam forming may be performed using Dirty PaperCoding (DPC). DPC is known to be the sum-rate capacity-achievingtechnique in Multiuser MIMO downlink. It is an extremely high complexityrandom non-linear coding technique primarily used as a theoreticalbenchmark. Implementation complexity of DPC led to the development ofless complex, linear techniques.

In some embodiments, beam forming uses MMSE transmit beam forming. Aweighted MMSE (WMMSE) approach is described in co-pending U.S. patentapplication Ser. No. 16/880,762, filed May 21, 2020, entitled“Beamformer computation taking into account non-homogeneity of offeredtraffic distribution among cells” incorporated herein in its entirety byreference.

In one embodiment, the throughput of the formed beams pointing at theservice areas is matched to the demand from those service areas. Thisgives additional flexibility in dealing with traffic distribution. Forexample, if a beam has less data to transmit, the spectral efficiency(SE) may be reduced at that beam by allowing more interference at thatbeam. This may increase the SE at beams with more data to transmit. Onepossible approach is to modify MMSE beamformer by including a weightmatrix on the MSE. In other words, error for the beams with less trafficcan be weighted less in comparison to beams with more traffic.

Scheduling

According to various embodiments, scheduling may be used to determine anillumination schedule and servicing of data queues as only subsets offeeds form clusters of beams are active within each transmissioninterval. In some embodiments, scheduling may proceed by first selectinga cluster of beam centers based on traffic loading, and then selecting aset of feeds to be used to form those beams. Clustering makes it harderto manage extreme peak-to-average traffic distributions, becauseservicing the high traffic queues creates trouble serving the lowtraffic queues with minimal latency. The system modeling uses “backpressure” to control traffic flow. Several scheduling variations such aspure clustering or split clustering may be used.

For pure clustering:

-   -   A single cluster is formed    -   A set of feeds used during a scheduling interval may be more or        less contiguous, and beams formed using that set of feeds are in        the general area illuminated by that set of feeds    -   In one embodiment, the cluster may be selected by first        selecting a beam with the deepest queue and then adding beams        that can be served by contiguous feeds of the antenna    -   Alternatively, the cluster may be selected by total traffic in        queues within a cluster region    -   In one embodiment, beams may be selected on a fixed reuse        pattern    -   In some embodiments, beams may be selected using a fixed or        randomized distance from previously selected beams

For split clustering

-   -   A set of feeds may be selected forming a single cluster as for        pure clustering, and in addition another subset or subsets may        be located elsewhere    -   This will allow flexibility to place additional beams (outside        of the cluster) to address high priority or latency sensitive        traffic    -   Contiguous feeds treated as above    -   Split feeds may be a number of isolated feeds or a number of        small clusters    -   Beams may be selected as above or according to the age of        packets in the service area queues    -   Any service area with the secondary pattern of the isolated feed        may be selected if the isolated feeds are far enough apart.

FIG. 14 is an exemplary scheduling flow chart according to oneembodiment.

FIG. 14 illustrates a Scheduler 1400 including a Cluster selection 1402,a Beam selection 1404 and a split 1412. A cluster may be selected (1402)by finding the service area with the most traffic in its queue. In oneembodiment, the area around a cluster center may be examined for totaltraffic. The criteria may be more than just traffic; it could include alatency metric and/or priority metric. After the cluster location isselected, the service areas within the cluster are chosen. These areasmay be constrained to lie on a fixed reuse pattern (static reuse 1434_,or they may be selected using a randomized reuse pattern referred to as“coin toss” (coin toss 1432). Beam selection 1404 may be constrained tobe within some distance of the cluster center.

A maximum number of beams (beam max 1428) is allowed as a systemparameter. If the selection method as described above results in fewerthan that maximum being chosen (summed 1430), the cluster may beextended. This is typically the case for odd-shaped areas such asFlorida.

The flow chart then indicates that SPLITs 1412 may be used. The idea isthat the clusters will tend to favor high traffic rather than latency.The SPLIT 1412 may chose an additional set of service areas that havetraffic that have been delayed (choose aged beams 1414). For example, 18feeds may be removed from the cluster (Remove cluster beams 1418) anddedicated to addressing the latency traffic. These would be individualfeeds, or they could be small groups of feeds (choose feeds 1420). Insome embodiments, Scheduler 1400 may cover more beams with isolatedfeeds 1422. The 1400 may then output the selected cluster, beams andfeeds to the GBBF (1424).

Soft Diversity

The GBBF approach allows the use of soft diversity on the feeder linkuplinks from the Gateway RFTs. This is highly preferred to a harddiversity. Hard diversity requires switching hardware on the satellite,but soft diversity does not require any switching. Soft diversity canmake use of the entire feeder link bandwidth during clear sky operation,whereas hard diversity cannot use the bandwidth from the diversegateways. The disadvantage of soft diversity is that some performance islost when the feeder links fade due to weather. This \effect has beenmodeled.

-   -   Select N random feeds out of 99, N ranges from 1 to 20    -   Select a UL (feeder link) deterministic fade depth X in the        range 1-20 dB applied to N feeds    -   In the absence of UL fade, UL C/N=20.52 dB, C/I=25.1 dB and        NPR=25.0 dB    -   The above three components combine to a C/(I+N)=18.2 dB (no        fade)    -   X dB fade reduces the UL RX signal power, reducing both UL C/N        and C/I by X dB        -   NPR=25.0 dB is kept fixed    -   Overall effect of C/N, C/I and NPR, i.e., C/N+I reduces as shown        in FIG. 15    -   This results in an increase in the noise level TX from that feed        -   Gain is increased to restore the faded feed signal to its            desired level        -   So, noise level is higher for the faded feeds on the DL TX    -   The increased noise level degrades spectral efficiency (SE) as        shown in FIG. 16.

FIG. 17 illustrates a method for beamforming according to variousembodiments.

In operation 1702, method 1700 provides a coverage area includingservice areas and data streams for each of the service areas. Theservice areas may tesselate the coverage area. In operation 1704, method1700 schedules N data streams of the data streams. In operation 1706,method 1700 selects a cluster of M feeds. In operation 1708, method 1700computes, with a GBBF processor (ground based beam former), M×N weights.In operation 1710, method 1700 generates M feed excitations bydistributing the N data streams per the M×N weights. In operation 1712,method 1700 switches an array to transfer a respective one of the M feedexcitations to a respective one of the M feeds. In operation 1714,method 1700 beamforms, with an antenna comprising the cluster, N beams.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artconsidering the above teachings. It is therefore to be understood thatchanges may be made in the embodiments disclosed which are within thescope of the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A method for beamforming comprising: selecting acluster of M feeds from feeds for a coverage area comprising serviceareas and data streams for each of the service areas; generating M feedexcitations by distributing N data streams per M×N weights; switching anarray to transfer a respective one of the M feed excitations to arespective one of the M feeds; and beamforming, with the M feeds of anantenna, N beams, wherein the N beams are each focused on a respectiveservice area of each of the N data streams, the M×N weights improvetransmitting into the respective service area of each of the N datastreams, and at least one of the N beams comprises a portion of aplurality of the M feed excitations.
 2. The method of claim 1, whereinthe antenna comprises an array-fed reflector comprising the feeds, and acount of the feeds is greater than M.
 3. The method of claim 1, whereinM is greater than N.
 4. The method of claim 1, wherein the M×N weightsare weighted to account for a predicted offered traffic demand based ona usage pattern for each of the N data streams.
 5. The method of claim1, wherein the selecting, the generating, the switching and thebeamforming are performed per an integral multiple of a transmissioninterval.
 6. The method of claim 1, wherein the beamforming moves the Nbeams over a breadth of the coverage area over a plurality oftransmission intervals.
 7. The method of claim 1, wherein the selectingcomprises a static mapping of clusters to a subset of service areas,wherein each subset comprises N service areas and each subset comprisesuniformly spaced service areas.
 8. The method of claim 1, wherein theselecting selects feeds associated with a respective service area of oneor more of the N data streams.
 9. The method of claim 1, furthercomprising forming the N data streams by encoding, modulating andframing each of the N data streams.
 10. The method of claim 1, furthercomprising sending the M feed excitations to a satellite, wherein theswitching and the beamforming are performed in the satellite, and thebeamforming comprises transmitting the N beams from the antenna.
 11. Themethod of claim 1, further comprising receiving the M feed excitationsfrom a satellite, wherein the switching and the beamforming areperformed in the satellite, and the beamforming comprises receiving theN beams from the antenna.
 12. The method of claim 1, wherein the M×Nweights provide interference suppression so that a same frequency andpolarization is used for the cluster of the M feeds.
 13. A system tobeamform comprising: a coverage area comprising service areas and datastreams for each of the service areas; a scheduler to select a clusterof M feeds from feeds; a GBBF processor (ground based beam former), tocompute M×N weights; a Complex Weight Multiplier to generate M feedexcitations that distribute N data streams per the M×N weights; and aswitch to transfer a respective one of the M feed excitations to arespective one of the M feeds, wherein N beams are beamformed with the Mfeeds of an antenna, the N beams are each focused on a respectiveservice area of each of the N data streams, the M×N weights improvetransmitting into the respective service area of each of the N datastreams, and at least one of the N beams comprises a portion of aplurality of the M feed excitations.
 14. The system of claim 13, whereinthe antenna comprises an array-fed reflector comprising more than the Mfeeds and M is greater than N.
 15. The system of claim 13, wherein theM×N weights are weighted to account for a predicted offered trafficdemand based on usage patterns for each of the N data streams.
 16. Thesystem of claim 13, wherein the Scheduler moves the N beams over abreadth of the coverage area over a plurality of transmission intervals.17. The system of claim 13, wherein the Scheduler comprises a staticmapping of clusters to a subset of service areas, wherein each subsetcomprises N service areas and each subset comprises uniformly spacedservice areas.
 18. The system of claim 13, wherein the Scheduler selectsfeeds associated with a respective service area of one or more of the Ndata streams.
 19. The system of claim 13, further comprising: asatellite; and a RF gateway to transmit the M feed excitations to thesatellite, wherein the switch and the antenna are disposed in thesatellite, and the antenna transmits the N beams.
 20. The system ofclaim 13, a satellite; and a RF gateway to receive the M feedexcitations from the satellite, wherein the switch and the antenna aredisposed in the satellite, and the antenna receives the N beams.